1. Field of the Invention
The present invention pertains to the art of rolling doors and, more particularly, to the use of a safety device on an electric steel rolling door which stops or reverses the direction of the door upon sensing of an obstruction to its path of movement.
2. Description of the Prior Art
In general, rolling doors, particularly typical electric steel rolling doors, utilize two electric motor driven sprocket gears which transfer the drive from the motor to a rotating main shaft at a predetermined drive ratio. The rotational direction of the main shaft determines whether the door is rolled to a storing position or unrolled to a closed position. Guide tracks are generally mounted on both sides of the electric steel rolling door and the door itself includes guide rollers which slide within the tracks.
In order to stop the rolling or unrolling of the door, some means must be provided to disconnect the current supplied to the electric motor. In the prior art, this function is generally performed by installing a microswitch in the sliding tracks which can be contacted by a lug mounted on the electric steel rolling door. By this arrangement, the activating lug on the steel rolling door will contact the microswitch which controls the current flow to the electric motor to thereby enable the steel rolling door to stop when moving downward or upward.
Although this type of known structural safety device attains the object of automatically stopping the door, there still exists considerable need for improvement with regard to attaining a higher degree of stopping accuracy. For instance, in operation such electric steel rolling door arrangements will permit the door to hit the uppermost frame member when raised rapidly or hit the ground when lowered at a fast rate. In addition, this type of safety stopping device does not enable automatic stopping of the rolling door in accidental situations such as when an obstruction is located in the path of the rolling door.
It is also heretofore been proposed to provide for stopping the movement of the rolling door when an obstruction is encountered. Such known arrangements include devices for sensing an excessive torque increase in the output of the electric motor. In addition, complicated safety devices have been proposed which include various sensors incorporated in the roller door assembly itself. These additionally known devices are expensive to manufacture and cannot be readily adapted for use on existing rolling door units which were made without an automatic stop safety system.
Therefore, a need exists in the art for a safety stopping device for use on electric rolling steel doors and the like which is relatively easy to manufacture, effectively provides automatic stopping or reversal of the rolling door upon sensing an obstruction and which can be readily adapted to existing rolling door arrangements not incorporating such safety devices.